Abstract
Mitochondrial transcription factor A (TFAM) is essential for the maintenance, expression and transmission of mitochondrial DNA (mtDNA). However, mechanisms for the post-translational ...regulation of TFAM are poorly understood. Here, we show that TFAM is lysine acetylated within its high-mobility-group box 1, a domain that can also be serine phosphorylated. Using bulk and single-molecule methods, we demonstrate that site-specific phosphoserine and acetyl-lysine mimics of human TFAM regulate its interaction with non-specific DNA through distinct kinetic pathways. We show that higher protein concentrations of both TFAM mimics are required to compact DNA to a similar extent as the wild-type. Compaction is thought to be crucial for regulating mtDNA segregation and expression. Moreover, we reveal that the reduced DNA binding affinity of the acetyl-lysine mimic arises from a lower on-rate, whereas the phosphoserine mimic displays both a decreased on-rate and an increased off-rate. Strikingly, the increased off-rate of the phosphoserine mimic is coupled to a significantly faster diffusion of TFAM on DNA. These findings indicate that acetylation and phosphorylation of TFAM can fine-tune TFAM-DNA binding affinity, to permit the discrete regulation of mtDNA dynamics. Furthermore, our results suggest that phosphorylation could additionally regulate transcription by altering the ability of TFAM to locate promoter sites.
We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q^{2}) up to 15.75 (GeV/c)^{2}. Combined with existing data, these provide an ...improved extraction of the proton magnetic form factor at high Q^{2} and double the range over which a longitudinal or transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q^{2} and attributed to hard two-photon exchange (TPE) effects, extending to 8 (GeV/c)^{2} the range of Q^{2} for which a discrepancy is established at >95% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q^{2}.
•Investigation on various intermetallics formed during solidification of Al2024 using thermal analysis.•Study the effect of cooling rate on solidification parameters of intermetallics in ...Al2024.•Using wide range of cooling rates to simulate solidification condition of Al2024 alloy.•Investigation on nucleation and growth of intermetallics at cooling rate used in DC casting.•Presenting a correlation between intermetallics nucleation temperature and cooling rate in Al2024.
The aim of this research is to determine intermetallic compounds formed in Al2024 alloy. The effect of cooling rates on solidification characteristics of intermetallic phases such as, nucleation and growth temperature, nucleation time and solid fraction have been determined via first derivative curve. The range of cooling rates used in this investigation is between 0.4 and 17.5°Cs−1. Thermal analysis was used to plot cooling curves and its derivative curves. Also, solid fraction versus time is plotted based on Newtonian technique. Microstructural evaluation and energy dispersive X-ray were used to identify intermetallic phases and their chemical composition. Formation of intermetallic compounds was interpreted through comparing the EDS analysis, binary and ternary diagrams, and the reactions detected from cooling curves. The results showed that nucleation and growth temperature of intermetallics was decreased by increasing of cooling rate. Also, the time intervals for the formation of intermetallic compounds were reduced.
The aim of this work was to investigate the effect of different cooling rates on the microstructure and solidification parameters of 2024 aluminum alloy. Solidification characteristics are recognized ...from the cooling curve and its first and second derivative curves which have been plotted using thermal analysis technique. In this study, a mold having high cooling rate was designed and used to simulate the direct-chill casting process. The results of thermal analysis show that the characteristic parameters of Al2024 alloy are influenced by cooling rate. The cooling rates used in the present study range from 0.4 to 17.5 °C s
−1
. Increasing the cooling rate affects the undercooling parameters both in liquidus and eutectic solidification regions. Investigations showed that solidification parameters such as nucleation temperature, recalescence undercooling temperature, and range of solidification temperature are influenced by variation of cooling rates. Microstructural evaluation was carried out to present the correlation between the cooling rate and dendrite arm spacing.
This study was undertaken to investigate the effect of Fe-rich intermetallics on the wear behavior of SAE F332 piston alloy. The wear behavior of Al–Si alloys was influenced by the presence of hard ...and brittle β-Al
5FeSi intermetallics. It was shown that an increase of iron from 0.15
wt% in the base alloy to about 0.7
wt% increased the hardness and improved the wear resistance by about 10% under applied loads of 20 and 40
N. Addition of iron up to 2.5
wt% further increased the hardness, however, it decreased the wear resistance by over 70% under the same applied loads. The negative effect of intermetallics was controlled via combined effects of high cooling rate solidification and strontium modification. The wear resistance of the controlled 1.2
wt% Fe alloy was improved by about 50% compared to the unrefined alloy with the same amount of iron under applied loads of 20 and 40
N.
Most research related to dendrite coherency point (DCP) has been done on cast aluminum alloys and at a low cooling rate condition. In this research, the DCP of a wrought aluminum alloy is calculated ...in the range of high cooling rates used in the direct-chill casting process. The two-thermocouple thermal analysis technique was used to determine the DCP of Al2024 alloy. The aim of this work is to investigate the effect of different cooling rates on the dendrite coherency characteristics of Al2024. The cooling rates used in the present study range from 0.4 to 17.5 °C s
−1
. Also, the effect of 1.2 wt pct Al-5Ti-1B grain refiner on the DCP was studied. To calculate the solid fraction at dendrite coherency, solid fraction versus time is plotted based on Newtonian technique. The results show that by increasing the cooling rate, both time and temperature of dendrite coherency are decreased. Also, by adding the Al-5Ti-1B master alloy, dendrite coherency temperature is reduced and dendrite impingement is postponed. To reduce casting defects occurring during equiaxed solidification,
e.g
., macrosegregation, porosities, and hot tearing, these two operations which lead to postpone the transition from mass to inter-dendritic feeding, or dendrite coherency, can be useful. By increasing the cooling rate, solid fraction at dendrite coherency increases initially and then decreases at higher cooling rates. Presence of grain refiner leads to increasing of solid fraction at DCP. Thus, by delaying the dendrite coherency and increasing the solid fraction at DCP, semi-solid forming can be performed on parts with higher solid fraction and less shrinkage. Microstructural evaluation was carried out to present the correlation between the cooling rate and solid fraction in 2024 aluminum alloy.
•Combined effect of Bi, Sb and Sr additions, and cooling condition was evaluated.•Two different scenarios of recalecense in response to cooling rate were observed.•Fraction solid increased in the ...order of Sr>Bi>Sb, corresponds to Si morphologies.•Only Bi decreased the nucleation temperature of Al2Cu eutectic phase.
Al–Si and Al–Cu eutectic phases strongly affect the properties of Al–Si–Cu cast alloys. The characteristic parameters of these two eutectic phases with addition of bismuth, antimony and strontium under different cooling rates (0.6–2°C/s) were investigated in ADC12 alloy using in situ thermal analysis. Results show that additives affect the Al–Si phase more than the Al–Cu (Al2Cu) phase. Addition elements showed two different scenarios in response to cooling rate in terms of recalescence of the Al–Si eutectic phase. Both Bi and Sb caused an increase in recalescence with increased cooling rate but Sr addition reduced the recalescence. Additions of Sb and Sr increased the nucleation temperature of Al2Cu, but addition of Bi produced an opposite effect. There seems to be relationship between the solidification temperature range and fraction solid of Al–Si and Al2Cu eutectic phases. As the cooling rate increases the fraction solid of Al–Si decreased and that of Al2Cu increased.
The effects of bismuth (Bi), antimony (Sb) and strontium (Sr) additions on the characteristic parameters of the evolution of aluminium dendrites in a near eutectic Al–11.3Si–2Cu–0.4Fe alloy during ...solidification at different cooling rates (0.6–2 °C) were investigated by computer-aided cooling curve thermal analysis (CA-CCTA). Nucleation temperature (
T
N
α
- Al
) is defined with a new approach based on second derivative cooling curve. The results showed that
T
N
α
- Al
increased with increasing cooling rate but both the growth temperature (
T
G
α
- Al
) and the coherency temperature (
T
DCP
) decreased. Increase in the temperature difference for dendrite coherency (
T
N
α
- Al
−
T
DCP
) with increasing cooling rate indicate a wider range of temperature before the dendrite can impinge on each other and higher fraction solid (
f
S
DCP
). Additions of Bi, Sb and Sr to the base alloy produced only a minor effect on
T
N
α
- Al
. Additions of Bi and Sb resulted in an increase in fraction solid and an increase of 30 % in the value of
T
N
α
- Al
−
T
G
α
- Al
to almost 13 °C.
Effect of different cooling rates and Al-5Ti-1B grain refiner on hot tearing susceptibility of Al2024 alloy were studied using thermal analysis. Influence of cooling rates on microsegregation, and ...the amount of gas and shrinkage porosities was investigated. The cooling rates used in the present study range from 0.4 to 17.5 K s
–1
. To evaluate the hot tearing susceptibility, Clyne and Davies’ criterion is used. To calculate solid fraction during solidification, solid fraction
vs
time is plotted based on Newtonian technique
via
thermal analysis. The results show that the hot tearing susceptibility reduces initially by increasing the cooling rate and then increases at higher cooling rates. Hot tearing susceptibility is decreased by grain refinement. Solidification characteristics of Al2024
e.g.,
microsegregation, gas, and shrinkage porosities are decreased by increasing cooling rate.
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